The present invention relates to a security device for a motor vehicle and, more particularly, to a coded surface acoustical wave (SAW) device that interacts with the ignition system of a motor vehicle.
Motor vehicles are susceptible to theft due to their relative high value and inherent transportability. Automobiles and trucks are especially attractive as objects of theft, as evidenced by an alarmingly high theft rate in many civilized countries.
The simplest security device has been the ignition key, which is relatively unique for each automobile corresponding thereto. However, professional thieves now duplicate such mechanical keys, by-pass ignition switches and/or remove the ignition apparatus from automobiles altogether in order to jump start them.
Heretofore, most systems for preventing theft of automobiles have been relegated to audible alarms signaling the attempted theft or break-in of the protected automobile. Certain mechanical and/or electronic interlocking devices have made it difficult for an automobile to be stolen by means of a standard ignition key alone. One such mechanical device comprises a tumbler lock and bar adapted to retain a steering wheel in a fixed position. The use of that system is, of course, cumbersome as well as time consuming.
Another interlocking device is a mechanical ignition key that contains resistive elements. Unfortunately, that system requires direct physical and electrical contact between the key and the electric sensor, which contact cannot always be guaranteed.
Recently, surface acoustic or acoustical wave (SAW) devices have been used to label certain items, such as objects for sale in retail establishments and individual inventory parts in warehouses. A SAW label system generally includes an interrogator for transmitting a first radio frequency (RF) signal and a SAW transponder which receives the signal, processes it and sends back a second RF signal containing encoded information. A receiver receives the second signal and decodes the information.
The transponder is nonpowered or passive. It receives the first (interrogating) signal as an input and produces the second (reply) signal as an output. Passive signal transforming means, within the transponder, converts the first signal to the second signal.
The transforming means includes signal conditioning elements coupled to receive the first signal from a transponder antenna. Each signal conditioning element provides an intermediate signal having a known delay and a known amplitude modification to the first signal. The transforming means also includes a signal combining element coupled to all of the signal conditioning elements for combining intermediate signals by addition or by multiplication to produce the second signal. The signal conditioning elements and the signal combining element impart a known informational code to the second signal which identifies the particular transponder. The second signal can be coupled out of the same antenna or a separate antenna for transmission as a reply.
Radiation, picked up by the antenna, is converted into electrical signals which are, in turn, converted into surface acoustic waves on the SAW device by a so-called leading transducer. These waves travel outwardly in opposite directions from opposite sides of the leading transducer and are then reconverted into electrical signals.
The aforementioned system is described in greater detail in U.S. Pat. No. 4,737,790 issued to Skeie et al. The system disclosed therein uses a voltage controlled oscillator to produce the first signal.
U.S. Pat. No. 4,625,208 issued to Skeie et al discloses a passive transponder for use in an interrogation system. A circuit is connected to transducer elements for supplying interrogating signals to the transducer elements and for receiving reply signals therefrom. Acoustic wave reflectors are provided to reflect the surface acoustic waves back towards the transducer elements.
As mentioned above, the systems disclosed in the aforementioned patents include a transmitter capable of transmitting RF pulses of electromagnetic energy. These pulses are received at the antenna of the transponder and applied to a piezoelectric leading transducer adapted to convert the electrical energy received from the antenna into acoustic wave energy in the piezoelectric material. Upon receipt of a pulse, an acoustic wave is generated within the piezoelectric material and is transmitted along a defined acoustic path.
Further transducers arranged at prescribed spaced intervals along this acoustic path convert the acoustic wave back into electrical energy thereby re-exciting the antenna of the transponder. The presence or absence of transducers at the prescribed locations along the acoustic wave path determines whether a reply pulse will be transmitted with a particular time delay in response to an interrogation pulse. This determines the informational code contained in the transponder reply.
When an acoustic wave pulse is reconverted into an electrical signal, it is supplied to an antenna on a transponder and transmitted as RF electromagnetic energy. This energy is received at a receiver and decoder, preferably at the same location as the interrogating transmitter, and the information contained in the response is decoded.
If SAW technology could be used for purposes other than mere identification of items, a significant improvement in security of valuable objects such as motor vehicles could be achieved.
A sophisticated security device is required for helping to ensure that an automobile may not be started and driven by one not authorized to do so.
It would be advantageous to provide a motor vehicle security system that would make it impossible to start the vehicle by using an unauthorized ignition key, or by by-passing the ignition switch or even by removing the switch assembly.
It would also be advantageous to provide a security system which does not require an electrical source of supply such as an electric battery.
It would also be advantageous to provide a security system which does not require electrical contact.
It would be advantageous to provide a SAW-based security system for discouraging theft of motor vehicles.
It would further be advantageous to provide a SAW-based security interlock system in the form of an ignition key.